Furnace emission remediation system

Abstract

A furnace exhaust remediation unit comprises an auxiliary combustion chamber with a gas burner assembly optimized for efficient and substantially complete combustion of pollutants, for example, waxy hydrocarbons emitted as binder/lubricant substances are driven off in sintering of green powdered-metal parts. The rate of flow of air and exhaust through the combustion chamber are controlled, permitting control of the average residence time of the emissions, ensuring substantially complete combustion. The burner is arranged such that it provides a high-energy exhaust stream directed tangentially into the combustion chamber, so that a spiral motion is provided to the combustible pollutants, improving mixing and heat transfer and thus ensuring efficient combustion of the vaporized hydrocarbon emissions.

What is claimed is:  
     
       1. An exhaust remediation system for combusting unburned combustible pollutants entrained in relatively low temperature exhaust streams, comprising: 
       a generally cylindrical combustion chamber including an insulated cylindrical shell defining an open inlet orifice and an open outlet orifice; said cylindrical combustion chamber defining an interior volume therein;  
       a fuel burner assembly, comprising a fuel nozzle, a control device for controlling supply of combustible fuel, means for igniting said fuel, and a blower for forcing a stream of ambient air around fuel issuing from said nozzle, so as to create a relatively high-temperature flame;  
       said fuel burner assembly being mounted to said combustion chamber, spaced from said open inlet orifice and aligned such that said high-temperature flame is directed substantially tangentially into said combustion chamber through said cylindrical shell and between said inlet orifice and said outlet orifice, not at the cylindrical axis thereof; and  
       means for controlling the rate at which one of both of ambient air and said exhaust stream flow into the inlet orifice of said combustion chamber; said means for controlling the rate being connected to said inlet orifice;  
       whereby the combination of said high-temperature flame and said exhaust stream traverses a generally spiral flow path within said cylindrical combustion chamber with said spiral flow path filling substantially said entire interior volume of said cylindrical combustion chamber; and wherein said unburned combustible pollutants experience a maximum average residence time in a portion of said combustion chamber that is heated by combustion of said fuel in said fuel burner assembly to a temperature sufficient to substantially combust said unburned combustible pollutants.  
     
     
       2. The exhaust remediation system of  claim 1 , wherein said combustion chamber is disposed with its cylindrical axis vertical, with its inlet orifice at its lower end and its outlet orifice at its upper end. 
     
     
       3. The exhaust remediation system of  claim 1 , wherein said unburned combustible pollutants experience a minimum average residence time of at least about 0.3-2.0 seconds in a portion of said combustion chamber that is heated to at least about 1200-1800° F. 
     
     
       4. The exhaust remediation system of  claim 1 , wherein said unburned combustible pollutants experience a minimum average residence time of at least about 0.4 seconds in a portion of said combustion chamber that is heated to at least about 1400° F. 
     
     
       5. The exhaust remediation system of  claim 1 , further comprising a thermocouple having a sensor disposed in said combustion chamber and connected to said control device for controlling supply of combustible fuel so as to maintain the temperature within said combustion chamber at a desired temperature. 
     
     
       6. The exhaust remediation system of  claim 1 , wherein said means for controlling the rate is a valve. 
     
     
       7. The exhaust remediation system of  claim 1 , wherein said open outlet orifice of said combustion chamber is spaced from a open mouth of a hood connected to a flue, such that ambient air can flow into said hood and flue, cooling the remediated exhaust stream passing into said flue. 
     
     
       8. A method for remediating exhaust streams by combusting unburned combustible pollutants entrained therein, comprising the steps of: 
       providing a exhaust remediation apparatus, including:  
       a generally cylindrical combustion chamber having an insulated cylindrical shell defining an open inlet orifice and an open outlet orifice and an interior volume therein,  
       a fuel burner assembly, comprising a fuel nozzle, a control device for controlling supply of combustible fuel, means for igniting said fuel, and a blower for forcing a stream of ambient air around fuel issuing from said nozzle, so as to create a relatively high-temperature flame, said fuel burner assembly being mounted to said combustion chamber and spaced from said open inlet orifice and aligned such that said high-temperature flame is directed substantially tangentially into said combustion chamber through said insulated cylindrical shell and between said inlet orifice and said outlet orifice, not at the cylindrical axis thereof, and  
       means for controlling the rate at which one of both of ambient air and exhaust flow into the inlet orifice of said combustion chamber;  
       mounting said exhaust remediation apparatus such that the exhaust to be remediated flows upwardly into the open inlet orifice of said combustion chamber; and  
       controlling the rate at which fuel is combusted by said fuel burner assembly, and the rate at which air is forced into said combustion chamber by said blower, thus controlling the temperature of said high-energy flame, with respect to the rate at which exhaust and ambient air are admitted to said combustion chamber, such that a spiral flow pattern of said furnace exhaust is established within said combustion chamber with said spiral flow path filling substantially said entire interior volume of said cylindrical combustion chamber, and such that said unburned combustible pollutants experience an average residence time within a portion of said combustion chamber at sufficiently high temperature that said unburned combustible pollutants are substantially combusted therein.  
     
     
       9. The method for remediating exhaust streams by combusting unburned combustible pollutants entrained therein of  claim 8 , wherein said combustion chamber is disposed such that its cylindrical axis is substantially vertical, with its inlet orifice at its lower end and its outlet orifice at its upper end. 
     
     
       10. The method for remediating exhaust streams by combusting unburned combustible pollutants entrained therein of  claim 8 , wherein the rate at which fuel is combusted by said fuel burner assembly with respect to the rate at which exhaust and ambient air are admitted to said combustion chamber, and the rate at which air is forced into said combustion chamber by said blower, are controlled such that said unburned combustible pollutants experience a minimum average residence time of at least about 0.3-2.0 seconds in a portion of said combustion chamber that is heated to at least about 1200-1800° F. 
     
     
       11. The method for remediating low energy exhaust streams by combusting unburned combustible pollutants entrained therein of  claim 8 , wherein the rate at which fuel is combusted by said fuel burner assembly with respect to the rate at which exhaust and ambient air are admitted to said combustion chamber, and the rate at which air is forced into said combustion chamber by said blower, are controlled such that said unburned combustible pollutants experience a minimum average residence time of at least about 0.4 seconds in a portion of said combustion chamber that is heated to at least about 1400° F. 
     
     
       12. The method for remediating low energy exhaust streams by combusting unburned combustible pollutants entrained therein of  claim 8 , wherein said exhaust remediation apparatus further comprises a thermocouple having a sensor disposed in said combustion chamber and connected to said control device, and comprising the further step of controlling supply of combustible fuel so as to maintain the temperature within said combustion chamber at a desired temperature. 
     
     
       13. The method for remediating low energy exhaust streams by combusting unburned combustible pollutants entrained therein of  claim 8 , comprising the further step of controlling the rate at which ambient air is admitted to said combustion chamber. 
     
     
       14. The method of  claim 13 , wherein said step of controlling the rate at which ambient air is admitted to said combustion chamber is performed by adjusting a valve disposed to control the size of the inlet orifice of said combustion chamber. 
     
     
       15. The method of  claim 14 , wherein said valve disposed to control the size of the inlet orifice of said combustion chamber is a slide gate valve. 
     
     
       16. The method of  claim 13 , wherein said step of controlling the rate at which ambient air is admitted to said combustion chamber is performed responsive to monitoring of said rate, by observing the disposition of airflow-responsive streamers disposed near said inlet orifice.